Hybrid imaging units are increasingly gaining importance in the field of medical imaging, this being so because they make it possible to be able to examine a patient in a very short time, sometimes even without repositioning, with the aid of two different modalities, that is to say to be able to compile image information with the aid of two different imaging devices. Such hybrid imaging units in this case include a first imaging device of relatively high spatial resolution, for example a computer tomograph or a magnetic resonance machine, and a second, in the present case, nuclear medicine imaging device of relatively high sensitivity for example for PET (position emission tomography) or SPECT (single photon emission computed tomography). Both methods are tomographic methods that show in the body the distribution of a radio nuclide, that is to say a radiopharmaceutical, given to the patient.
Such radio nuclides have the property of accumulating intensively at specific pathological zones. PET or SPECT imaging methods by mixing the acquisition of the radio nuclide distribution in the body, while corresponding images that finally show probability distributions and constitute an “activity card” can be determined from the acquired measurement signals and displayed. The mode of operation of these methods is known in principle, and there is no need to go into this in more detail.
It is particularly expedient to combine a first imaging device in the form of a magnetic resonance machine with a second imaging device in the form of a PET device. The point is that magnetic resonance tomography permits a very high spatial resolution, on the one hand, while not influencing PET measurement, on the other hand. As a result, it is possible to erase the PET detectors in the interior of the cylindrical patient aperture of a conventional magnetic resonance system such that both can measure using the same isocenter, and is even possible for both measurements to run simultaneously. The PET examination furthermore delivers very informative images, and this is to be ascribed to the production of the measurement signals (time-resolved detection of gamma quanta). What is involved here is a coincidence measurement method of high counting yield and thus of very high sensitivity.
Both the highly resolved image of the first imaging device, that is to say, for example, the MR image, and that of the second imaging device, that is to say, for example, the PET image, permits a subsequent evaluation with the aid of which it is possible to draw diagnostic conclusions that then require a follow-up examination in some cases, in order, for example, to examine again more precisely with the aid of the magnetic resonance machine a specific region displayed as relevant in the PET image. This is certainly directly possible in principle, but is time consuming. The imaging unit can consequently not be visualized optimally since it is occupied up to the end of the evaluation of the first image recording until it has been decided whether a follow-up examination is necessary or not.